This proposal describes a five-year career development program to prepare the candidate, Dr. Michael Coronado, for a career as an independent scientist. This program will expand Dr. Coronado's scientific background in cardiovascular research by providing technical training and expertise in mitochondrial and myocardial biology. Dr. Coronado's mentor is Dr. Daniel Bernstein, the Salter Endowed Professor of Pediatrics (Cardiology) at Stanford University. Dr. Bernstein is an expert in myocardial G protein coupled receptor signaling, director of Stanford's Myocardial Biology T32 Training Grant, former Chief of Pediatric Cardiology, and has over two decades of experience mentoring young scientists. The K99 phase of the grant will provide the necessary intellectual background and training to foster Dr. Coronado's successful transition from a mentored postdoctoral fellow into an independent scientist. This will be accomplished by developing four essential characteristics of an independent scientist including: (1) unique technical skills, methodologies and tools, (2) the ability to conceptualize scientific questions and generate hypothesize-driven experiments, (3) communication and collaborative skills and (4) mentorship and laboratory management skills. These characteristics will be developed through performing the novel research described in this proposal, receiving mentorship from an expert advisory committee, participating in courses and workshops and mentorship of students and postdocs. Dr. Coronado's long-term scientific career goal is to establish a research program to further investigate the mechanisms by which mitochondrial function and dynamics are regulated in cardiovascular health and disease. Preliminary studies by Dr. Coronado show a close connection between ?-adrenergic receptors (ARs) and mitochondria, both of which play a unique dual role in regulating both cardiac energetics and cell death. Mitochondria are the principal source of energy for cardiac contraction, and ?-ARs, the major regulators of cardiac energy demand. During exercise, mitochondria must quickly respond to increased energy demands. Since ?-ARs are responsible for regulating the rate and strength of contraction, it is logical that they also regulate the signaling pathways that enable the cell to meet acute energetic demands. Mitochondria are also key regulators of apoptosis, a consequence of excessive ?-AR stimulation, suggesting another connection between ?-ARs and mitochondrial dynamics. Dr. Coronado's preliminary studies show that activation of the ?1- AR both pharmacologically (in vitro) and with exercise (in vivo) results in fragmented mitochondria with enhanced respiration. A key observation is that pharmacological inhibition of Drp1-mediated mitochondrial fragmentation results in significantly decreased exercise capacity and an early shift towards anaerobic pathways of ATP generation. The current paradigm considers fragmented mitochondria as pathological, an indicator of poor mitochondrial health and usually associated with decreased respiration, increased reactive oxygen species generation and apoptotic induction. However, our data suggests that mitochondria can also use the process of fragmentation to respond to increased energy demand. Dr. Coronado proposes that mitochondrial fragmentation in this state is physiological and a response to hemodynamic demands. He proposes to revise current paradigms by defining the role of physiological mitochondrial fragmentation and the mechanisms by which it is regulated, including the idea that ?-ARs regulate mitochondrial function and dynamics in response to energetic demand. Dr. Coronado will build on his preliminary findings by determining the mechanisms connecting ?-AR signaling, mitochondrial dynamics and energetic homeostasis. To date, he has developed a background in mitochondrial biology through externships with leaders in the field including Dr. Doug Wallace at the University of Pennsylvania and Dr. Roberta Gottlieb at Cedars-Sinai. During the K99 phase of the grant, Dr. Coronado will complete Specific Aim 1, which will determine the mechanisms by which ?-ARs differentially regulate mitochondrial dynamics. Specific Aim 2 will be carried out during the independent R00 phase and will focus on the novel role of physiologic fragmentation in cardiovascular dynamics and the mechanisms by which ?-ARs mediate physiological mitochondrial fragmentation vs. pathological mitochondrial fragmentation. Dr. Coronado will make use of the physiologic phenotyping and cell signaling expertise in Drs. Bernstein and Mochly-Rosen, as well as continue collaborations with Drs. Wallace and Gottlieb to gain new skills and methodologies through yearly externships. Dr. Coronado's ultimate goal is to explore novel mechanisms that regulate cardiac bioenergetics and identify new drug targets for treating heart failure. In summary, the proposed studies will challenge existing paradigms about the role of mitochondrial fragmentation in the heart and examine new mechanisms of mitochondrial regulation by ?-ARs. Completing these studies in a strong mentored environment will lay the foundation for Dr. Coronado's transition to his own independent research program.